With the spread of the Internet, it has now become possible to receive various services, such as purchasing content and reserving tickets, via networks. These services are of various types, ranging from free services easily accessible by anyone to charged services available exclusively to members. In order to use those services that are provided to specific users, including services exclusive to members, it is necessary to perform personal authentication by using an ID that identifies an individual and authentication information that confirms the identification. Passwords are widely used as authentication information for this purpose. Some types of services may involve users' personal information, in which case biometric, IC-card, or some other type of more advanced authentication information is desirable. When such advanced authentication information is used, a terminal with a special interface for entry of the authentication information becomes necessary. However, the number of home information appliances that are connectable to networks is increasing, and these home information appliances will be increasingly used to access services through networks. A problem that arises in this situation is that home information appliances typically have user interfaces inferior to those of personal computers, so it takes more time and effort to enter authentication information for personal authentication through the user interfaces, making the appliances hard to use. Another problem is that if advanced authentication information is used with home information appliances, it becomes necessary to equip all home information appliances with special interfaces for entry of authentication information, which would be impractical for appliances with many cost constraints.
A known solution to this problem, when a server must authenticate a terminal not having any authentication information shared with the server, is for the server to generate authentication image data and send it to the terminal; after the terminal displays the image data, an authentication terminal sharing authentication information with the server captures the image and sends the captured image together with the authentication terminal's authentication information to the server; the server analyzes the received information, checking that the information includes the image data the server generated itself and the authentication information that should be held by the authentication terminal, thereby enabling authentication of the terminal that had no authentication information (see, for example, Patent Document 1).    Patent Document 1: Japanese Patent Application Publication No. 2005-78371 (pp. 7-8, FIG. 1)